Process for coating paper



May 16, 1950 CHARLES R. OUTTERSON BENJAMIN A. FORD Patented May 16, 1950 FFICE rnocsss FOR-COATING rarna I Charles R. Outterson and 'Beniamin 'A. Ford, Richmond, Va., assi'gnors to Albemarle Paper Manufacturing Company, Richmond, van, a corporation of Virginia Application October 14, 1946, sci-m No. 103,200

This invention relates to improved methods of and apparatus for applying coating compositions topaper and similar sheet materials.

The object of this invention is to provide a method of coating paper whereby said coating will be evenly distributed and substantially free from the usual marks and blemishes.

Another object is to provide a uniform, unblemished coating of any desired thickness.

Still a further object is to provide a method of coating paper whereby the amount of coating applied and fixed to the paper may be accurately regulated.

A further object is to provide an apparatus for coating paper which will accomplish the above objects simply and efficiently.

Other objects will become apparent hereinafter from the description and the drawings.

It will be understood that the coating compositions referred to are the usual types employed in the manufacture of certain kinds of paper where it is desirable to apply a mineral coating to the paper web. Such coating compositions generally comprise aqueous suspensions of flnely divided minerals such as clay, calcium carbonate, tita-" nium dioxide and the like. If desired an adhesive such as casein or starch may be added to the coming procedure which may be accomplished by means of brushes, rolls, knives and the like. Such secondary spreading operations, however, have a disadvantageous tendency to mark the paper with an undesirable pattern. This coated paper is frequently marred by brush marks, or by ridges and ripples from smoothing rolls, or by drag marks from doctor blades.

In order to obtain a more or less uniform coating by the above means it has generally been found advisable to apply an excess oiv the coating composition and then to remove such excess by 2 Claims. (01. 11744) We have discovered that a coating which is of uniform thickness and substantially free of undesirable markings maybe obtained simply and economically by passing the coated paper web over a suitably inclined path while the coating composition is still fluid. Under these conditions the mobile coating flows into a smooth, uniform layer. Furthermore our unique spreading means permits the application of accurate, metered quantities of coating composition to the paper web. Still a further advantage of our invention is separate wiping means such as doctor rolls or doctor blades, which are usually also the spreading means.- It ls'somewhat dimcult by this method to regulate the weight of coating applied to the paper web. However, even where a measured quantity of oatlng omposition is initially applied to the paper web, the use of secondary spreading means above described leaves undesirable markings.

the fact that coatings of any desired thickness may be successfully applied.

Referring to the drawings:

Figure l is a diagrammatic representation in elevational view of the essential parts of an apparatus which may be used in carrying out our invention; I

Figure 2 is a diagrammatic view showing a modification of the apparatus; and

- Figure 3 is a diagrammatic view showing still another modification. i

In carrying out our invention, fluidcoating composition, preferably in predetermined or metered quantity, is applied to one surface of a paper web. The quantity of coating applied to the web may be varied to give any desired weight of coating. The web is immediately carried past a suitable spreading and leveling means whichacts uniformly across the width of the web and spreads the fluid coating layer thereon. When the coated web leaves said spreading means, the coating will have the undesirable markings incidental to the use of such means. These markings are smoothed out by passing the web with its still fluid coating over a path inclined at a suitable angle. Under the influence of gravity and cohesion forces the ridges and other elevated portions in the mobile coating flow out thus leaving a smooth evenly distributed layer. After the coating is thus spread and smoothed, the coated p" per web is dried by any suitable means.

For the successful operation of our process, it is essential that the coating composition remain wet and mobile until after the smoothing operation on the inclined path is completed. This ma be accomplished by regulating the concentration of solids in the coating composition. A composition having a moderate concentration of solids is preferable because of the tendency of the paper web to absorb the water vehicle from the coating. If the concentration of solids is moderate, sumcient fluid will remain in the coatlag, even after absorption by the paper web, to leave the coating in a mobile state.

It is also preferable to employ a paper body stock which is moderately water repellent since a highly absorbent paper may. remove so much sufllcient magnitude to permit flow of the still" mobile coating composition into depressions in the surface of the coating, but not so large that it will cause too rapid a backward flow of the coating. The angle of the path is determined by such factors as the viscosity and drying rate of the coating medium, the absorbency of the paper being coated and the speed with which the coated web is passed over the path.

In Figure l which shows a typical means for carrying out our process, a paper web I is used 150 feet per minute over spring roll 3, through calendars 4, under and around guide rolls 5. Roll 6, which dips into a bath 1 of fluid coating composition, having a moderate concentrationof solids and a viscosity of 55-57 Kreb units tested by the Stormer method, applies the composition to side B of the web. By varying the rotational speed of. roll 8, a metered quantity is deposited. The uncoated surface A Of the web then passes immediately around breast roll 8. The coated surface is then subjected to the action of spreading roll 9 which spreads and levels the still fluid coating. Roll 9 may be driven at any desired speed either in the direction of the paper or in a reverse direction. The uncoated surface A of the web then passes over guide rolls III which are mounted in such a fashion that the web moves along inclined path II. at an angle of 60 with the horizontal as shown. The coating composition is still in amobile state as the web moves alongthe inclined path so that gravitational and cohesion forces cause the coating to fiow into an evenly distributed layer, thus smoothing away the ridges and other undesirable markings left by the spreading roll. The coated web is then carried to a suitable dryer I 2 in which the coating is dried sufllciently not to be marked before it contacts guide roll l3. The web is further dried by passage over dryers ll.

In. the modification shown in Fig. 2, web la having surfaces A and B is'moved more slowly through coating apparatus than the web shown in the embodiment of Fig. l. The web passes over guide rolls 5:! and then around guide roll l8 which provides a rigid backing for the web at the point where a metered amount of coating isapplied to surface B by roll l5 which dips into vat Ia containing the fluid coating composition. The desired weight of coating is deposited on the web by varying the amount of pressure in the nip.

4 The web with its coating still fiuid is then carried past a suitable rigid spreading means I! and then over guide rolls Ilia along inclined path I la which forms a 29 angle as shown with the horizontal The coated web is then dried and finished in any conventional way.

Fig. 3 shows a modification in which web lb is moved more rapidly through the coating apparatus than the webs shown in the embodiments of Figs. 1 and 2. For such speeds we have found it advantageous to employ an inclined path ilb which makes an angle of 67 with the horizontal as shown.

It is obvious from the above description that any suitable means may be employed to apply I a metered quantity of coating composition to the paper web. It is also obvious that any suitable spreading means may be used to level the coating before it enters on the inclined path.

It will be understood that although the above description discloses practical and preferred embodiments of our invention, various modifications are possible which fall within the scope of the appended claims.

We claim:

1. The process of coating paper which comprises applying a relatively viscous mobile aqueous coating composition as a coating over one face of a continuously moving web, advancing the web with the coated face uppermost, while said coating is still mobile, upwardly along a path which is inclined at an angle greaterthan that at which said viscous coating composition will remain in repose, whereby said coating composition flows by gravity reversely to the travel of the web, correlating the speed of movement of the web with the rate of flow and the setting rate of the coating composition,- whereby mobility of the coating composition during said gravity flow continues until smoothing is completed, and moving the web along said inclined path until the surface of the coating is smoothed by said gravity flow.

2. The process. of coating paper which comprises applying and spreading a relatively viscous mobile aqueous coating composition as a coating of a predetermined thickness over one face of a continuously moving web, advancing the web with the coated face uppermost, while said coating is still mobile,'upwardly along a path which is inclined at an angle greater than that at which said viscous coating compositionwill remain in repose, whereby said coating composition flows by gravity reversely to the travel of the web, correlating the speed of movement of the web with the rate of flow and the setting rate of the coating composition, whereby mobility of the coating composition during said gravity flow continues until smoothing is completed, and moving the web along said inclined pa'th until the surface of the coating is smoothedby said gravity flow.

CHARLES R. OUI'IERSON. BENJAMIN A. FORD.

nnrnnnncns ,crrnn The following references are of record in the file of this patent:

. UNITED STATES PATENTS Number 2,229,921 Gofi Jan. 28, 1941 

1. THE PROCESS OF COATING PAPER WHICH COMPRISES APPLYING A RELATIVELY VISCOUS MOBILE AQUEOUS COATING COMPOSITION AS A COATING OVER ONE FACE OF A CONTINUOUSLY MOVING WEB, ADVANCING THE WEB WITH THE COATED FACE UPERMOST, WHILE SAID COATING IS STILL MOBILE, UPWARDLY ALONG A PATH WHICH IS INCLINED AT AN ANGLE GREATER THAN THAT AT WHICH SAID VISCOUS COATING COMPOSITION WILL REMAIN IN REPOSE, WHEREBY SAID COATING COMPOSITION FLOWS BY GRAVITY REVERSELY TO THE TRAVEL OF THE WEB, CORRELATING THE SPEED OF MOVEMENT OF THE WEB WITH THE RATE OF FLOW AND THE SETTING RATE OF THE COATING COMPOSITION, WHEREBY MOBILITY OF THE COATING COMPOSITION DURING SAID GRAVITY FLOW CONTINUES UNTIL SMOOTHING IS COMPLETED, AND MOVING THE WEB ALONG SAID INCLINED PATH UNTIL THE SURFACE OF THE COATING IS SMOOTHED BY SAID GRAVITY FLOW. 